Stable modulation index calibration and dynamic control
Calibrating a Gaussian frequency-shift keying modulation index includes generating a training sequence of bits, shaping a pulse from the training sequence according to an initial modulation index, and converting the shaped signal to a transmission signal. The transmission signal is then either looped through a radio frequency core or processed by frequency deviation estimation hardware to determine a frequency deviation. The frequency deviation is converted to a new modulation index, and potentially a ratio between a target modulation index and a measured modulation index as a scaling factor. The process is then iteratively repeated until a threshold frequency deviation is achieved.
1. A system for wireless communications with Gaussian frequency-shift keying (GFSK), the system comprising:
a signal generator configured to generate training bit sequences;
a pulse shaping element configured to generate shaped signals from the training bit sequences and a modulation index value;
a baseband transmitter configured to generate transmission signals from the shaped signals;
a frequency deviation estimator configured to determine frequency deviations of the transmission signals; and
a modulation index value estimator configured at least to:
in a first iteration, determine a first updated modulation index value based on a first frequency deviation, update the modulation index value used by the pulse shaping element, and calculate a first ratio of the modulation index value to the first updated modulation index value; and
in a second iteration, determine a second updated modulation index value based on a second frequency deviation, update the modulation index value used by the pulse shaping element, and calculate a second ratio of the modulation index value to the second updated modulation index value.
2. The system of claim 1 , further comprising a radio frequency core configured to receive the transmission signals and to loop back the transmission signals to the frequency deviation estimator.
3. The system of claim 1 , wherein the first ratio and the second ratio are used as scaling factors by the pulse shaping element.
4. The system of claim 1 , wherein the modulation index value estimator is further configured to calculate an average frequency deviation based on the first frequency deviation and the second frequency deviation.
5. The system of claim 1 , wherein the training bit sequences are generated with increasing lengths in successive calibration operations.
6. The system of claim 1 , wherein the modulation index value estimator is configured to perform the first iteration and the second iteration periodically to correct drift over time.
7. The system of claim 1 , wherein the modulation index value estimator is configured to perform the first iteration and the second iteration when temperature change is detected by the system.
8. The system of claim 1 , wherein the modulation index value estimator is configured to perform the first iteration and the second iteration when aberrant signals are received by the system.
9. The system of claim 1 , wherein the modulation index value estimator is configured to perform the first iteration and the second iteration at start-up of the system.
10. A method for modulation index calibration in a wireless communication system with Gaussian frequency-shift keying (GFSK), the method comprising:
generating training bit sequences;
generating shaped signals from the training bit sequences and a modulation index value;
generating transmission signals from the shaped signals;
determining frequency deviations of the transmission signals;
in a first iteration, determining a first updated modulation index value based on a first frequency deviation, updating the modulation index value, and calculating a first ratio of the modulation index value to the first updated modulation index value; and
in a second iteration, determining a second updated modulation index value based on a second frequency deviation, updating the modulation index value, and calculating a second ratio of the modulation index value to the second updated modulation index value.
11. The method of claim 10 , further comprising looping back the transmission signals through a radio frequency core.
12. The method of claim 10 , wherein generating the shaped signals comprises using the first ratio and the second ratio as scaling factors.
13. The method of claim 10 , further comprising calculating an average frequency deviation based on the first frequency deviation and the second frequency deviation.
14. The method of claim 10 , wherein generating the training bit sequences comprises generating the training bits sequences with increasing lengths in successive calibration operations.
15. The method of claim 10 , wherein the first iteration and the second iteration are performed periodically to correct drift over time.
16. The method of claim 10 , wherein the first iteration and the second iteration are performed when temperature change is detected by the wireless communication system.
17. The method of claim 10 , wherein the first iteration and the second iteration are performed when aberrant signals are received by the wireless communication system.
18. The method of claim 10 , wherein the first iteration and the second iteration are performed at start-up of the wireless communication system.